(1) Field of the Invention
The present invention relates to a liquid crystal display device and its manufacturing method, particularly to an art to be effectively applied to an in-plane field type active-matrix liquid crystal display device.
(2) Description of the Prior Art
An active-matrix liquid crystal display device using an active element such as thin film transistor (TFT) has been widely spread as a display terminal of OA equipment because it is thin and lightweighted and has a high image quality equal to that of a cathode-ray tube.
The display system of the active-matrix liquid crystal display device is roughly divided into the following types.
One of them is a type, in which a liquid crystal layer is enclosed between a pair of substrates with two transparent electrodes formed on the substrates, a driving voltage is applied to the transparent electrodes, thereby driving the liquid crystal layer by an electric field almost perpendicular to the surfaces of the substrates, and the light passing the transparent electrodes and entering the liquid crystal layer is modulated (hereafter referred to as a vertical field type). Every product spread at present uses this type.
However, an active-matrix liquid crystal display device using the vertical field type has the problems on practical use that a contrast of an image extremely varies when changing viewing angles and particularly, a gradation level is inverted depending on a viewing angle when displaying half tone images.
The other of them is a type, in which a liquid crystal layer is enclosed between a pair of substrates, a driving voltage is applied to two stripe-like or line-like electrodes formed on either or both of the substrates, thereby driving a liquid crystal layer by an electric field almost parallel with the surfaces of the liquid crystal layer, and the light entering the liquid crystal layer from the gap between the two electrodes is modulated (hereafter referred to as an in-plane field type).
An active-matrix liquid crystal display device using the in-plane field type can realize wide viewing-angle characteristics. However, any active-matrix liquid crystal display device using the in-plane field type is not practically used yet.
Features of an active-matrix liquid crystal display device using the in-plane field type are shown in the official gazettes of Japanese Patent Application No. 505247/1993, Japanese Patent Publication No. 21907/1988, and Japanese Patent Laid-Open No. 160878/1994.